The aforementioned specification discloses methods and apparatus for producing novel textile fabrics. In a preferred embodiment, textile fibers are needled together into an integral structure with a face surface and back surface and having coherent fiber entanglement. The needled structure has a high overall bulk density and a bulk density gradient in which the bulk density increases from the back surface to the face surface, i.e., the bulk density is greater at the face surface than at the back surface. A plurality of layers of fibers are superimposed on one another, e.g., by carding of staple fibers, to form a web of loosely matted fibers having a needle pick-up gradient which increases in the Z direction, i.e., from the back surface to the face surface. The web is needled until a resulting structure has an overall bulk density of at least six pounds per cubic foot, e.g., at least eight to twelve pounds per cubic foot, and the ratio of the bulk density at the back surface to the bulk density at the face surface is in the range of at least 1:2 to as high as 1:8, preferably 1:3 to 1:5. Also, the fabric has a controlled axis of flexure which lies at least within 0.4, e.g., 0.3, and especially 0.2 or 0.1, of the distance from the face surface to the back surface. Some of the fiber entanglement includes fibers being oriented into closely spaced rows of fiber chain entanglement, the rows extending lengthwise of the structure. The bulk density gradient of the needled structure may be accomplished by positioning a plurality of superimposed layers of staple fibers so that the average fiber denier and/or length of the fibers of the layers decreases from the back surface to the face surface, the average fiber deniers being 1/2 or less up to 8 or more, especially to 5, and the average fiber length being 3/4 inch or less up to 4 inches or more, especially 1 inch to 3 inches. Further, bulk density of the needled structure may be accomplished by laying on the face surface of the needled structure a web of at least one layer of relatively short loosely matted fibers (less than 2 inches, e.g., 1/16 to 3/4 inch) and needling the short fibers to increase the bulk density of the structure to at least 10 pounds per cubic foot, e.g., 12 pounds per cubic foot, and produce a dense region of bulk density higher than the bulk density of the remaining portion of the needled structure. The axis of flexure of the needled structure will lie close to, e.g., within or adjacent to the dense region.
Preferably, the structure is then relaxed, e.g., mechanically relaxed, to loosen the structure and adjust the modulus thereof. It is also preferred that the structure be further densified by shrinking the fibers at and adjacent to the face surface to define a compacted region of higher bulk density near the face surface. The fibers at and adjacent to the face surface are, accordingly, at least in part shrinkable fibers (heat and/or solvent shrinkable), and densification may be accomplished by applying heat or solvents to the face surface (while maintaining the back surface relatively cool when heat shrinking. This product may be used for many purposes, but the fabric is preferably impregnated with a filler to further raise the overall bulk density of the fabric and provide higher densities. Also, the filled fabric may be used for many purposes without further processing. Alternately, the filled fabric may be finished by mechanical processes such as buffing, working, sanding and embossing or chemical processes such as adding softeners, sizes, or applying a conventional finish material, e.g., a leather finish, to the face surface. The filler is disposed within the open interstices between the fibers of the needled fabric, and the filler is preferably an elastomer, e.g., natural rubber, in the form of solid particles, especially clusters of particles which are predominantly loosely bonded to the fibers. The filler is disposed in the fabric in an amount insufficient to fill all the interstices between the fibers, e.g., between 10% and 200% of the weight of the fibers in the needled structure. The filled fabric preferably has overall bulk densities of between 20 and 60 pounds per cubic foot, although densities outside of this range may be accomplished, if desired.
It is further preferred that the needled structure have an overall bulk density of at least 12 pounds per cubic foot, a ratio of density at the back surface to the density at the face surface of at least 1:2, and be impregnated with the filler to provide overall densities of between about at least 25 pounds per cubic foot, e.g., 30-45 pounds per cubic foot, or more, e.g., up to 50 pounds per cubic foot.
The addition of the filler to the needled structure is made in such a manner so as to at least preserve the bulk density gradient of the needled structure, i.e., with the bulk density increasing from the back surface of the needled structure to the face surface thereof. Preferably, however, the filler is added to the needled structure so that not only is the bulk density gradient preserved but that the bulk density gradient of the filled fabric is increased, i.e., the filler is preferentially disposed toward the face surface of the fabric. This preferential disposition of filler is illustrated in the photomicrograph of the filled fabric in the parent application.
Preferential disposition of the filler in the needled structure, according to an embodiment of the parent application, is accomplished by contacting the needled structure with a liquid filler composition (latex emulsion in the preferred embodiment) and then passing the structure between counter-rotating rolls to lightly squeeze the structure and produce add-ons of liquid filler composition which are less than saturation amounts. When the needled structure contains less than saturation amounts of the liquid filler composition, i.e., the voids in the structure are not filled by the liquid filler composition, capillary action will move the liquid filler composition toward the face surface of the needled structure where the fibers are more densely entangled, i.e., the average space between fibers is less than in any other portion of the needled fabric. Stated in another way, the liquid filler composition will inherently migrate by capillary action toward the portion of the needled structure where the fibers are in a closer spaced relationship, i.e., toward the more dense portions of the structure. Thus, when the liquid filler composition is coagulated and cured, dried, etc., in that preferential disposition, the filled fabric has an increased bulk density gradient from the back surface to the face surface beyond that provided by the needled structure alone.
As disclosed in the aforementioned parent application, the filler in the needled structure provides a hand and feel and increased density and support for surface finishes, which are advantageous in producing the artificial leathers of the parent application. The filler also provides additional suppleness and shape retention properties to the needled structure so as to prevent collapse of the interstices between individual fibers when the fabric is used. Further, as disclosed in a co-pending application Ser. No. 403,059, entitled FABRIC WITH THIN SURFACE MATRIX AND METHOD FOR PRODUCTION THEREOF, filed on Oct. 3, 1973, (the entire disclosure of which is incorporated herein by reference and relied upon), the filler aids in embossing the fabric to produce a surface matrix resembling leather.